The objective of the proposed research is to develop and use the techniques of gas chromatography-mass spectrometry and high-pressure liquid-chromatography to analyze DNA-modification and its biological role. DNA from various organisms will be examined for the nature/level of methylated (or otherwise modified) bases (e.g., 5-methylcytosine, N6-methyladenine, 1,-3, or -7 methylguanine). Among the systems to be investigated are: (1) the mealybug (to study the connection between DNA modification and facultative heterochromatization); (2) the sea urchin (to study the connection between DNA modification and differentiation), (3) rat mammary tumors (to study the connection between DNA modification and tumor induction, and the role of hormones in these processes). In addition, we will examine DNAs from unicellular eukaryotes, as well as from bacterial and animal viruses.